I've been having a problem with my iMac i7 (mid 2010) for quite awhile. Any kind of restart from a software update, or a user selected restart, causing the iMac to get stuck on the restart gray screen with the rotating loading "carat."
If I power down the machine, then turn it back on it, it boots up fine.
Internal hard drive checks out fine.
I took it to the Apple Store Genius bar, and they could not find anything physically wrong with it, and blamed it on a problem with my user (software), thinking since the OS has been transferred over from several previous machines (an iMac G4 and then a PowerMac G5), that something PowerPC is causing the freeze.
I've tried doing a verbose mode, but not seeing anything.
Any ideas on how to further diagnose this and ultimately fix it so I can restart without having to power down and then back on?